1. Field of the Invention
This invention relates to a motor vehicle lock with a latch and a ratchet, the latch being movable out of a fully latched position into a release position and vice versa, the ratchet being movable out of an engagement position which keeps the latch in the fully latched position into a raised position which releases the latch, and optionally, into an overtravel position and vice versa. Preferably, a motorized drive being provided for movement of the ratchet. The motor vehicle lock is especially suited as a rear hatch lock, but can also be used as a side door lock, rear door lock or hood lock.
2. Description of Related Art
A known motor vehicle lock (U.S. Pat. No. 5,020,838 A) has a ratchet and a latch which are connected to one another by means of a spring. The spring is arranged such that the ratchet is loaded in the direction of its engagement position. When the ratchet is moved by means of a motorized drive into its raised position, the spring loads the latch in the direction of the release position of the latch. This is intended to ensure that the latch is reliably opened. However, opening is not reliable, for example, when the door is iced over and the motor vehicle door therefore is not pressed by the door seal in the direction of the open position. The latch is then held by the lock pin in its fully latched position and the ratchet is moved back into the engagement position as a result of the spring force. Thus, under certain circumstances, reliable opening is not possible.
In order to prevent the ratchet from re-engaging the engagement position after completed lifting of the ratchet, providing a mechanical lever, a so-called snow load lever, on the motor vehicle lock is known. The snow load lever engages relative to the ratchet when the raised position of the ratchet is reached, such that the ratchet is held in the raised position until the latch has reached its release position. In this position of the latch, the snow load lever is pivoted free of the ratchet so that it is operable again with respect to the fully latched position of the latch. This mechanical technology is proven and advantageous since it solves the problem of a hatch or a door which does not open itself, for example, when loaded by snow, when the reset force of the seal is not enough, or when the seal is frozen solid. However, the additional lever constitutes an additional cost factor and additional risk factor (jamming, breaking, etc.).
The re-engagement of the ratchet with the engagement position can be precluded using purely control engineering for ratchets which are driven by a motor. To do this, it is necessary to scan the motion of the latch by means of microswitches until the release position is reached. However, this version is both expensive and fault-susceptible.
Moreover, a motor vehicle lock is known (U.S. Patent Application Publication No. 2004/0227358 A1, which is commonly owned with the present application) in which the force or work which is to be applied for release of the latch is minimized. This is achieved in that the ratchet interacts with ratchet kinematics and the latch is not held directly by the ratchet in its fully latched position, but indirectly by means of the ratchet kinematics. In this motor vehicle lock, there are no special provisions for reliable opening when the door is iced up. The disclosure of U.S. Patent Application Publication 2004/0227358 A1 is hereby incorporated by reference.
The motor vehicle lock for multi-catch motor vehicle locks (U.S. Pat. No. 5,934,717 A) which forms the starting point of this invention calls for a ratchet which can return to the engagement position only after the latch moves into the release position. This is accomplished in that the ratchet with the latch in the preliminary catch position has an overlap and the ratchet is made such that it can return again to the engagement position by its motorized drive only after the latch is shifted into the release position. Here, the overlap between the latch and ratchet is made such that scanning of the ratchet by sensors can be omitted. However, the disadvantage here is that this concept can only be used for multi-catch motor vehicle locks. Moreover, when the doors are frozen tight, an increased force must be applied by the operator to open a motor vehicle door.